Biomechanical Strain Responses in the Optic Nerve Head Region in Glaucoma Patients After Intraocular Pressure Lowering

Abstract

Objective To measure strain values and their association with intraocular pressure (IOP) change across five posterior eye regions in glaucoma patients. Design Cohort study. Participants Glaucoma patients who were imaged with optical coherence tomography (OCT) prior to and after laser suturelysis following trabeculectomy surgery (29 image pairs, 26 persons) Intervention Noninvasive imaging of the eye. Main Outcomes Strain values in eye regions. Results Mean strains were lowest in the retina and highest in the prelaminar neural tissue (PLNT) for Emax, Γmax, and Ezz. The values of Emax in the anterior lamina cribrosa (ALC) and sclera were significantly related (P=0.0094, linear regression). Higher axial strain (Ezz) was significantly associated with greater IOP decrease in the ALC, PLNT, and retina (P<0.05). Higher Γmax and Emax strains were significantly associated with greater IOP decreases across all 5 eye regions. ALC and PLNT had negative median radial (Err) compliance, while sclera had positive Err compliance (P=0.017). Emax and Γmax strains of the ALC were significantly and positively associated with these strains in the other 4 regions (P<0.005). Likewise, the Ezz of ALC had a significant positive relationship with the other 4 regions (P<0.05). Conclusions Regional strains in the optic nerve head zone can be effectively measured using OCT and are related to the magnitude of IOP change. Strains were largest in PLNT and ALC and were smallest in retina. The sclera and choroid on average expand radially and circumferentially indicating a volume increase with IOP lowering.